New Insights into the Generation of Singlet Oxygen in the Metal-Free Peroxymonosulfate Activation Process: Important Role of Electron-Deficient Carbon Atoms

• Published in: Environmental science & technology Vol. 54; no. 2; pp. 1232 - 1241
• Main Authors: Gao, Yaowen, Chen, Zhenhuan, Zhu, Yue, Li, Tong, Hu, Chun
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 21.01.2020
• Subjects: Activation; Bisphenol A; Carbon; Carbon nitride; Catalytic activity; Electron paramagnetic resonance; Electrons; Environmental degradation; Industrial wastes; Industrial wastewater; Nitrogen; Oxidation; Oxidation process; Oxygen; Peroxides; Photoelectron spectroscopy; Photoelectrons; Pollutants; Reaction kinetics; Reactive oxygen species; Singlet Oxygen; Wastewater; Wastewater treatment
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.9b05856

A nonradical oxidation process via metal-free peroxymonosulfate (PMS) activation has recently attracted considerable attention for organic pollutant degradation; however, the origin of singlet oxygen (1O2) generation still remains controversial. In this study, nitrogen-doped carbon nanosheets (NCN-900) derived from graphitic carbon nitride were developed for activation of PMS and elucidation of 1O2 production. With a large specific surface area (1218.7 m2 g–1) and high nitrogen content (14.5 at %), NCN-900 exhibits superior catalytic activity in PMS activation, as evidenced by complete degradation of bisphenol A within 2 min using 0.1 g L–1 NCN-900 and 2 mM PMS. Moreover, the reaction rate constant fitted by pseudo-first-order kinetics for NCN-900 reaches an impressive value of 3.1 min–1. Electron paramagnetic resonance measurements and quenching tests verified 1O2 as the primary reactive oxygen species in the NCN-900/PMS system. Based on X-ray photoelectron spectroscopy analysis and theoretical calculations, an unexpected generation pathway of 1O2 involving PMS oxidation over the electron-deficient carbon atoms neighboring graphitic N in NCN-900 was unraveled. Besides, the NCN-900/PMS system is also applicable for remediation of actual industrial wastewater. This work highlights the important role of electron-deficient carbon atoms in 1O2 generation from PMS oxidation and furnishes theoretical support for further relevant studies.